The present invention relates to workpiece conveyance apparatus and more specifically to a method of supplying workpieces to workstations using an autoloader.
Workpiece conveyance apparatus are commonly used in manufacturing facilities to transfer workpieces to and from workstations and/or between workstations within a manufacturing process. One particular type of workpiece conveyance apparatus that is used is an apparatus known as an autoloader. An autoloader typically includes a conveyance apparatus with a gripping device that is mounted to a guidance structure and is movable along the length of the guidance structure. The gripping device is operable to load and unload workpieces to and from workstations.
Autoloaders are commonly used in a machining line, wherein a sequence of machining operations are performed on a workpiece by different types of workstations. Usually, a plurality of workstations for performing a particular machining operation are provided. An example of a machining line that uses autoloaders is the machining line for a crankshaft, wherein a raw or unfinished crankshaft from a casting operation is subjected to a series of turning, grinding, tapping, drilling and polishing operations.
Conventionally, a machining line often includes one or more sub-lines, wherein a single autoloader is used to supply workpieces to workstations that perform different machining operations. In such a mixed operation sub-line, when a workstation for a particular machining operation stops for any reason, the entire sub-line stops. Moreover, the sub-line cycle time is limited to the longest operation cycle time. In order to remedy this inefficiency, a machining line has been developed, wherein the machining line includes a plurality of zones or segments dedicated to a particular machining operation. In each such segment, an autoloader moves workpieces to and from a plurality of workstations that perform the same operation. For a particular zone having workstations MC1, MC2, MC3, the autoloader is controlled to supply workpieces to the workstations in the fixed sequence MC1, MC2, MC3, which is continuously repeated, eg. MC1, MC2, MC3, MC1, MC2, MC3, etc. With this control scheme, the cycle time of the segment is dependent upon the workstation with the longest cycle time. Moreover, if one of the workstations stops (because of a fault or otherwise), the autoloader stops.
Accordingly, there is a need in the art for a more efficient method of supplying workpieces to workstations using an autoloader. The present invention is directed to such a method.